1988 100hp merc ignition coils

Amor

Cadet
Joined
Jun 5, 2003
Messages
8
Is it possible for a faulty spark plug wire or coil to send a spike signal back through your switch box and blow it?
 

Spidybot

Lieutenant Commander
Joined
Apr 4, 2002
Messages
1,734
Re: 1988 100hp merc ignition coils

No, should be impossible. Circuits are separated so unless something is broken and allows for connection. If the high voltage current is lead through the box by accident (like somebody checking for spark by drawing ground from the box's casing) it might happen.
 

12Footer

Fleet Admiral
Joined
Mar 25, 2001
Messages
8,217
Re: 1988 100hp merc ignition coils

That depends. It should not harm the cd if the spark plug is grounded, or say, the plug wire is arcing to ground. But if a plug fouls, a plug wire falls off, leaving no destination for the pulse to go, yes, it could 'find' the nearest ground. This could be thru the dialectric compound poured around the coil to the frame of the motor, which could damage it.<br />Old tv sets used to suffer early deaths sometimes, due to dust giving a conductive path accross an area that was not where it was to go. As soon as an arc occured, the path it took, would have a nice path made of carbon (conductive) from the HV output to ground.<br />You may have heard this in a tv that got wet. a snapping would be heard, or a sound like water on a hot pan.<br />Your manual will warn "not to disconnect a plug wire and allow the motor to run, as damage to the HVCD unit may occur".<br />A bad plug wire, or arcing could make an engine run poorly tho for sure, and also allow the plug to foul,and then the poor path to ground can ruin stuff.
 

Amor

Cadet
Joined
Jun 5, 2003
Messages
8
Re: 1988 100hp merc ignition coils

Thanks. The problem is the motor is only running on two cylinders, it won't go over 2000rpm's. The switch box has been replaced twice. It works for a few minutes after being replaced and then cuts out again. Obviously something is burning out the switch box. The ignition coils spark fine, but I am thinking there is a short in the coil wire which is sending the charge back and burning out the switch box. What else could it be?
 
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